When communication is performed between different networks in a network system including a plurality of networks, it is necessary to set in advance routing parameters indicating relay information in a relay apparatus that performs relay for the networks. In a relay apparatus in the past, the routing parameters are manually set. Therefore, knowledge concerning the networks is necessary in setting the routing parameters. It is likely that a communication error is caused by a setting mistake of the routing parameters.
Therefore, as a method of performing communication between different networks in a control network system including a plurality of control networks, there is proposed a method of performing communication not depending on routing parameters by providing a communication path database in which network numbers and station numbers that communication passes from a start point station to an end point station of the communication are described in the order of the passage and describing path information extracted from the communication path database in a communication message (Patent Literature 1).
There is also proposed a method of creating routing tables of stations on a network by issuing, after establishing a control network system, a routing table creation command for creating a routing table from a station that is in a state in which a routing table is settable (Patent Literature 2).